1. Field of the Invention
The invention relates to a phototherapy device for treatment of skin disorders by irradiation with UV radiation in the UV-B range (280 nm to 320 nm).
2. Description of Related Art
Among skin disorders there are various conditions, such as psoriasis, atopic dermatitis, vitiligo and the like. In this section, psoriasis is described as a typical example. The mechanism of psoriasis is still not clarified. Some treatment methods have been proposed for it, and they are applied. However, no therapy has been found for complete healing of diseased sites of all patients. The aforementioned treatment methods are used only to suppress the outbreak of the disorder. These therapy methods are largely classified in three methods, specifically topical remedies, phototherapy and oral remedies.
In topical remedies, generally steroid medicine for topical application, vitamin D3 pharmaceuticals and the like are used. Steroid medicines for topical use lead to dermal atrophies and the like when used over a long time. Vitamin D3 pharmaceuticals for topical application must be used with consideration of daily application frequencies and the like.
As oral remedies, retinoid, cyclosporin, and the like are used. These pharmaceuticals for oral application suppress anomalous proliferation of the skin and weaken immune reactions. Therefore, they have the disadvantage that they act not only on diseased sites, but also outside of diseased sites. As a result, it is difficult to use them for treatment of patients with especially severely diseased sites.
In phototherapy, there is a process using UV-A (320 nm to 400 nm) and a process using UV-B. The therapy process using UV radiation in the UV-A range is generally called PUVA therapy, it being used together with a photosensitive pharmaceutical called psoralen. After oral or topical use of psoralen, or after bathing in a psoralen-containing liquid, UV radiation in the UV-A range is applied, with the consequence of difficulties in daily life, such as sun after therapy and the like must be avoided. The therapy process using UV-B range is conversely a simple process in which treatment can be performed without using psoralen. Recently, a narrow-band UV-B method therapy has been noted in which diseased sites are irradiated only with an especially effective UV-B wavelength range.
The UV light source in narrow-band UV-B therapy is a fluorescent lamp with spectral lines at 311 nm to 313 nm. The appearance and basic arrangement of the fluorescent lamp are identical to those of fluorescent lamps for general illumination purposes. Only the types of phosphors for converting UV radiation from mercury vapor which is contained in the fluorescent lamp into other wavelengths differ from one another. Phosphor-containing gadolinium as the activating agent is used as this phosphor. Expressed conversely, sharp emission spectra of 311 nm to 313 nm are radiated because phosphor-containing gadolinium as the activating agent is used. There is also, to some extent, an indication of the possibility of increasing the therapy effect at a somewhat shorter wavelength, for example, at an emission wavelength of about 305 nm. However, since essentially there is no phosphors in this range which emits intensively, in practice, narrowband UV-B therapy using a fluorescent lamp with spectral lines at 311 nm to 313 nm is performed.
In view of this situation, a new light source for narrow-band UV-B therapy has been suggested. There is a XeCl excimer lamp using XeCl excimer radiation in which the individual peak wavelength is 308 nm. FIGS. 5(a) & 5(b), each show an emission spectrum example of this light source. The characterizing feature thereof is that the wavelength peak is at 308 nm, and that short wavelengths of less than 300 nm are also emitted, as is radiation with short wavelengths which are not emitted in a fluorescent lamp for narrow-band UV-B therapy. Whether this radiation with short wavelengths acts effectively is not completely clear. To some extent, however, it has already been reported that, at diseased sites at which no therapy effect was confirmed with a conventional fluorescent lamp, therapy effects were confirmed by the XeCl excimer lamp. Phototherapy with a XeCl excimer lamp is disclosed in International Patent Application Publication WO 03/024526 A and U.S. Pat. No. 5,955,840.
In addition to the above described therapy effect, the XeCl excimer lamp also has the following advantages. Within the fluorescent lamp the UV radiation from the mercury which has been heated and vaporized during operation by the discharge is converted by the phosphors into emissions from 311 nm to 313 nm so that the intensity changes depending on the degree of vaporization of the mercury which is liquid prior to operation. In narrow-band UV-B therapy, the duration of irradiation is at most a few minutes each time. The intensity within a few minutes after the start of lamp operation changes by some 10%, by which control of the duration of irradiation of the diseased site is difficult. On the other hand, the XeCl excimer lamp, due to the gaseous state of lamp contents before operation, has a slight change of intensity after the start of lamp operation so that control of the duration of the irradiation of diseased sites is simple.
Compared to a fluorescent lamp, the XeCl excimer lamp can be operated with a higher power density so that diseased sites can be irradiated with a high illuminance. This means that, in this connection, a shortening of the duration of therapy can be expected. Since diseased sites are irradiated with a constant amount of irradiation in a well controlled manner, the patient is prohibited from moving the diseased sites during the therapy duration. Shortening of the length of therapy is therefore an important improvement for reducing the burden on the patient.
As was described above, in the phototherapy device (hereinafter phototherapy device using excimer radiation) in the UV-B range with a light source which is a XeCl excimer lamp, the radiant light from the lamp has an individual peak wavelength of 308 nm because excimer emission is used for this purpose. The potential of this device as a phototherapy device which is effective for treatment is being considered.
It is mentioned that light in the UV-B range which is effective for treatment of skin disorders has two aspects, specifically the therapy effect and side effects (harm). One side effect relates to formation of erythemas on the skin. The above described phototherapy device using excimer radiation carries out radiation with two aspects: specifically, the therapy effects and side effect (harm) since the spectrum with an individual peak wavelength has a wide emission range with FWHM (full width at half maximum) of at least 20 nm. On the other hand, since the emission in the vicinity of 310 nm has a negligibly small side effect, while the therapy effect is also weak, therapy was performed by irradiation over a long time interval. Recently, it has become increasingly clear that UV radiation with shorter wavelengths has a greater therapeutic effect. Furthermore, it has been found that there are cases in which, depending on individually differences of symptoms of skin disorders, UV radiation in the UV-B range in the vicinity of 310 nm has hardly any therapeutic effect.